The invention relates to a method of manufacturing combustion type photoflash lamps provided with a shatterproof sleeve of organic plastic material for integration into automated mass production of combustion type photoflash lamps. These combustion type photoflash lamps comprise a vitreous envelope which contains a filling of finely divided combustible material and a combustion-sustaining gas, more particularly oxygen. As is well known, the vitreous envelope shatters during the combustion process due to the pressure wave, and due to high thermal loading of the envelope. To inhibit scattering of fragments of shattered glass, the vitreous envelope of conventional lamps presently in use is covered with a tough lacquer coating which holds together the fragments of the shattered lamp envelope in its original shape.
While in case of the well-known combustion type photoflash lamps with a bulb volume of about 4 cubic centimeters and an oxygen pressure of from 1000 to 2000 torr, a coating prepared by one immersion into a lacquer bath affords sufficient protection from shattering, it is necessary in case of small size combustible photoflash lamps with a bulb volume of 1 cc and less and a respectively increased oxygen pressure of e.g. 5-15 atmospheres, to repeatedly immerse the bulbs in order to produce a reliable shatterproof coating. During the intervals between the individual working steps of immersion, the lacquer coating must be relieved from the solvent by drying.
The immersion procedure takes its time and, because of the use of inflammable solvents, it cannot be integrated into automated mass production. Moreover, it is expensive as the solvents cannot be recovered at a reasonable expenditure.
Another drawback of applying a shatterproof sleeve by lacquer coating is also mainly observed in case of small size lamp envelopes. For these applying a uniform coating with lacquer meets with difficulties. Shatterproof coatings of irregular thickness for these subminiature photoflash lamps can lead to so-called "exploders", i. e. the lamps blow up during the combustion process.
Another drawback of lacquer-coated subminiature type photoflash lamps is the formation of bubbles in the lacquer coating during combustion and the possible expansion of the coating. This enlargement of volume of the lacquer-coated photoflash lamp is liable to complicate the removal of flashed lamps, for instance, in flashguns incorporated in cameras or, to impair lamp transfer in multiflash devices.
To overcome these drawbacks, it has become known to place the vitreous envelope of a photoflash lamp in a shatterproof sleeve designed as a plastic capsule and matching the lamp shade.
The pre-shaped plastic capsule resembling a cap can be made from a heat-shrinking material which, subsequent to shrinking, closely abuts the envelope.